Technological Field
The present invention relates to an image inspection apparatus and an image inspection apparatus control program and, in particular, to a technology for appropriately inspecting image formation using roll paper.
Description of the Related Art
In an electrophotographic image forming system, an inspection apparatus having therein a reader is arranged on a downstream side of an image forming apparatus such that a printing abnormality in a printed matter is inspected from an image obtained by reading a sheet after the image formation.
Incidentally, in an image inspection apparatus for inspecting an image printed by an image forming apparatus in an in-line fashion, in the case of cut paper such as fixed form paper, the leading edge of the conveyed sheet is sensed by a photosensor such that the reading timing is specified as a timing after a predetermined time using this sensing signal as a trigger and a sub-scanning image area signal (V_Valid (hereinafter abbreviated as VV) signal) is generated. Here, the period during which the VV signal is turned on is a period for executing inspection of an image.
On the other hand, in the case of roll paper, printing is started from a state in which the roll paper is passed from a paper feeding apparatus to a paper discharging apparatus for the roll paper. For this reason, there is a problem in how to generate the sub-scanning image area signal which specifies the scanner timing of the image inspection apparatus without the concept of the leading edge of the sheet like the cut paper.
In addition, since the image forming apparatus and the image inspection apparatus are configured as different systems, the image forming timing and the reading timing are in an asynchronous relationship. Here, the clock frequency at which a circuit is moved is different between the respective apparatuses. Besides, even if the clock frequency at which the circuit is moved is notationally the same frequency in the respective apparatuses, the clock frequencies do not completely coincide because these apparatuses are asynchronous.
Therefore, if there is even a minute timing difference of less than one clock between the image forming timing and the reading timing when the reading timing is designated in the image inspection apparatus by some technique, it is supposed that, in the case of the roll paper which continues to form an image for several hundred meters, an error between the image forming timing and the reading timing accumulates to result in a large value. As a result, the reading position (timing) gradually deviates with respect to the printing position of the sub-scanning, which eventually results in a deviation to the extent that influences the inspection.
Note that, in the case of the above-mentioned cut paper, since the sub-scanning image area signal is generated by sensing the leading edge of the sheet, the accumulation of the error can be reset for each sheet of the cut paper and the accumulation of the error as in the roll paper has no influence.
In addition, as related technologies of this type, various related proposals have been made in JP 2016-107429 A and JP 1999-058698 A.
JP 2016-107429 A has made proposals regarding a nonuniform sheet conveyance speed and a reading cycle in image inspection on the roll paper. Here, only reading requiring positional accuracy is concerned because the reading cycle=the exposure time is satisfied and the reading cycle is generated based on sheet conveyance information from the image forming apparatus. However, no proposal has been made regarding “asynchronicity between the image forming apparatus and the image inspection apparatus” which is treated as an issue in the present application.
JP 1999-058698 A has proposed to control the turning on and off of an exposure lamp by using a rotary shaft of a printing roll (conveyance roller) as an encoder. However, a proposal regarding the reading start position corresponding to the printing start position in the case of the roll paper has not been mentioned.
That is, the generation of the sub-scanning image area signal for appropriately reading the print image in the image inspection apparatus that reads an image formed on the roll paper is neither mentioned nor suggested in any document of JP 2016-107429 A and JP 1999-058698.